Nonlinear optical effects manifested by electromagnetic induced transparency in cold atoms

This dissertation reports experimental studies of nonlinear optical effects manifested by electromagnetically induced transparency (EIT) in cold Rb atoms. The cold Rb atoms are confined in a magneto-optic trap (MOT) obtained with the standard laser cooling and trapping technique. Because of the near zero Doppler shift and a high phase density, the cold Rb sample is well suited for studies of atomic coherence and interference and related applications, and the experiments can be compared quantitatively with theoretical calculations. It is shown that with EIT induced in the multi-level Rb system by laser fields, the linear absorption is suppressed and the nonlinear susceptibility is enhanced, which enables studies of nonlinear optics in the cold atoms with slow photons and at low light intensities. Three independent experiments are described and the experimental results are presented. First, an experimental method that can produce simultaneously co-propagating slow and fast light pulses is discussed and the experimental demonstration is reported. Second, it is shown that in a three-level Rb system coupled by multi-color laser fields, the multi-channel two-photon Raman transitions can be manipulated by the relative phase and frequency of a control laser field. Third, a scheme for all-optical switching near single photon levels is developed. The scheme is based on the phase-dependent multi-photon interference in a coherently coupled four-level system. The phase dependent multi-photon interference is observed and switching of a single light pulse by a control pulse containing ∼20 photons is demonstrated. These experimental studies reveal new phenomena manifested by quantum coherence and interference in cold atoms, contribute to the advancement of fundamental quantum optics and nonlinear optics at ultra-low light intensities, and may lead to the development of new techniques to control quantum states of atoms and photons, which will be useful for applications in quantum measurements and quantum photonic devices.

In vivo characterization of myocardial tissue post myocardial infarction using combined fluorescence and diffuse reflectance spectroscopy

Accurately assessing the extent of myocardial tissue injury induced by Myocardial infarction (MI) is critical to the planning and optimization of MI patient management. With this in mind, this study investigated the feasibility of using combined fluorescence and diffuse reflectance spectroscopy to characterize a myocardial infarct at the different stages of its development. An animal study was conducted using twenty male Sprague-Dawley rats with MI. In vivo fluorescence spectra at 337 nm excitation and diffuse reflectance between 400 nm and 900 nm were measured from the heart using a portable fiber-optic spectroscopic system. Spectral acquisition was performed on (1) the normal heart region; (2) the region immediately surrounding the infarct; and (3) the infarcted region—one, two, three and four weeks into MI development. The spectral data were divided into six subgroups according to the histopathological features associated with various degrees/severities of myocardial tissue injury as well as various stages of myocardial tissue remodeling, post infarction. Various data processing and analysis techniques were employed to recognize the representative spectral features corresponding to various histopathological features associated with myocardial infarction. The identified spectral features were utilized in discriminant analysis to further evaluate their effectiveness in classifying tissue injuries induced by MI. In this study, it was observed that MI induced significant alterations (p < 0.05) in the diffuse reflectance spectra, especially between 450 nm and 600 nm, from myocardial tissue within the infarcted and surrounding regions. In addition, MI induced a significant elevation in fluorescence intensities at 400 and 460 nm from the myocardial tissue from the same regions. The extent of these spectral alterations was related to the duration of the infarction. Using the spectral features identified, an effective tissue injury classification algorithm was developed which produced a satisfactory overall classification result (87.8%). The findings of this research support the concept that optical spectroscopy represents a useful tool to non-invasively determine the in vivo pathophysiological features of a myocardial infarct and its surrounding tissue, thereby providing valuable real-time feedback to surgeons during various surgical interventions for MI.

Material Synthesis and Characterization on Low-Dimensional Cobaltates

In this thesis, results of the investigation of a new low-dimensional cobaltates Ba2-xSrxCoO 4 are presented. The synthesis of both polycrystalline and single crystalline compounds using the methods of conventional solid state chemical reaction and floating-zone optical furnace is first introduced. Besides making polycrystalline powders, we successfully, for the first time, synthesized large single crystals of Ba2CoO4. Single crystals were also obtained for Sr doped Ba2-xSrxCoO 4. Powder and single crystal x-ray diffraction results indicate that pure Ba2CoO4 has a monoclinic structure at room temperature. With Sr doping, the lattice structure changes to orthorhombic when x ≥ 0.5 and to tetragonal when x = 2.0. In addition, Ba2CoO4 and Sr2CoO4, have completely different basic building blocks in the structure. One is CoO4 tetrahedron and the later is CoO6 octahedron, respectively. Electronic and magnetic properties were characterized and discussed. The magnetic susceptibility, specific heat and thermal conductivity show that Ba2CoO4 has an antiferromagnetic (AF) ground state with an AF ordering temperature TN = 25 K. However, the magnitude of the Néel temperature TN is significantly lower than the Curie-Weiss temperature (:&thetas;: ∼ 110 K), suggesting either reduced-dimensional magnetic interactions and/or the existence of magnetic frustration. The AF interaction persists in all the samples with different doping concentrations. The Néel temperature doesn't vary much in the monoclinic structure regime but decreases when the system enters orthorhombic. Magnetically, Ba2CoO4 has an AF insulating ground state while Sr2CoO4 has a ferromagnetic (FM) metallic ground state. Neutron powder refinement results indicate a magnetic structure with the spin mostly aligned along the a-axis. The result from a μ-spin rotation/relaxation (μ+SR) experiment agrees with our refinement. It confirms the AF order in the ab -plane. We also studied the spin dynamics and its anisotropy in the AF phase. The results from inelastic neutron scattering show that spin waves have a clear dispersion along a-axis but not along c-axis, indicating spin anisotropy. This work finds the strong spin-lattice coupling in this novel complex material. The interplay between the two degrees of freedom results an interesting phase diagram. Further research is needed when large single crystal samples are available.

Synthesis and characterization of photochromic indolyl substituted fulgides and fulgimides

The fulgide and fulgimide family constitutes an important class of organic photochromic compounds. The ability of fulgides and fulgimides to interconvert between two key forms by irradiation of different wavelength of light has made them promising material in optical memory devices, optical switches and sensors, and specialty dyes and inks. Thermal stability and hydrolytic stability of fulgides and fulgimides are essential for their practical applications. A deuterated trifluoromethyl indolylfulgide was synthesized based on the synthetic pathway of the proteo trifluoromethyl indolylfulgide using commercially available deuterated starting materials. Deuteration of the isopropylidene group improved the thermal stability of the indolylfulgide by a factor of 7. ^ Fulgimides are the most important fulgide derivatives. Fulgimides improve the hydrolytic stability of fulgides by replacing the succinic anhydride ring with a succinimide ring. A novel trifluoromethyl N-ethoxycarbonylmethyl indolylfulgimide was synthesized from trifluoromethyl indolylfulgide. The trifluoromethyl indolylfulgide was synthesized on a large scale in five steps with an overall yield of 18%. The indolylfulgide was then converted to indolylfulgimide by aminolysis follow by dehydration. The N-ethoxycarbonylmethyl indolylfulgimide showed enhanced hydrolytic stability and photochemical stability in 70/30 ethanol/water. ^ Three novel aqueous soluble fulgimides, trifluoromethyl carboxylic acid indolylfulgimide, dicarboxylic acid indolylfulgimide, and H-carboxylic acid indolylfulgimide, were synthesized. In sodium phosphate buffer (pH 7.4) at 37 ºC, an unusual hydrolysis of the trifluoromethyl group of the closed form of the carboxylic acid indolylfulgimide resulted in the dicarboxylic acid indolylfulgimide which has an additional carboxylic acid group. The closed form of dicarboxylic acid indolylfulgimide was further decarboxylated to generate H-carboxylic acid indolylfulgimide which was not photochromic. The trifluoromethyl dicarboxylic acid indolylfulgimide is the most robust fulgimide yet reported in aqueous solution. ^ A novel aqueous soluble methyl carboxylic acid indolylfulgimide was synthesized from methyl indolylfulgide. The methyl indolylfulgide was synthesized in five steps with an overall yield of 21%. The methyl carboxylic acid indolylfulgimide was synthesized by aminolysis follow by dehydration. The methyl carboxylic acid indolylfulgimide is expected to have improved thermal and photochemical stability in aqueous solutions relative to the trifluoromethyl analog.^

Chemical characterization of dissolved organic nitrogen in an oligotrophic subtropical coastal ecosystem

Water samples were collected from rivers and estuarine environments within the Florida Coastal Everglades (FCE) ecosystem, USA, and ultrafiltered dissolved organic matter (UDOM; 1 kDa) was isolated for characterization of its source, bioavailability and diagenetic state. A combination of techniques, including 15N cross-polarization magic angle spinning nuclear magnetic resonance (15N CPMAS NMR) and X-ray photoelectron spectroscopy (XPS), were used to analyze the N components of UDOM. The concentrations and compositions of total hydrolysable amino acids (HAAs) were analyzed to estimate UDOM bioavailability and diagenetic state. Optical properties (UV–visible and fluorescence) and the stable isotope ratios of C and N were measured to assess the source and dynamics of UDOM. Spectroscopic analyses consistently showed that the major N species of UDOM are in amide form, but significant contributions of aromatic-N were also observed. XPS showed a very high pyridinic-N concentration in the FCE–UDOM (21.7 ± 2.7%) compared with those in other environments. The sources of this aromatic-N are unclear, but could include soot and charred materials from wild fires. Relatively high total HAA concentrations (4 ± 2% UDOC or 27 ± 4% UDON) are indicative of bioavailable components, and HAA compositions suggest FCE–UDOM has not undergone extensive diagenetic processing. These observations can be attributed to the low microbial activity and a continuous supply of fresh UDOM in this oligotrophic ecosystem. Marsh plants appear to be the dominant source of UDOM in freshwater regions of the FCE, whereas seagrasses and algae are the dominant sources of UDOM in Florida Bay. This study demonstrates the utility of a multi-technique and multi-proxy approach to advance our understanding of DON biogeochemistry.

In Vivo Characterization of Myocardial Tissue Post Myocardial Infarction Using Combined Fluorescence and Diffuse Reflectance Spectroscopy

Accurately assessing the extent of myocardial tissue injury induced by Myocardial infarction (MI) is critical to the planning and optimization of MI patient management. With this in mind, this study investigated the feasibility of using combined fluorescence and diffuse reflectance spectroscopy to characterize a myocardial infarct at the different stages of its development. An animal study was conducted using twenty male Sprague-Dawley rats with MI. In vivo fluorescence spectra at 337 nm excitation and diffuse reflectance between 400 nm and 900 nm were measured from the heart using a portable fiber-optic spectroscopic system. Spectral acquisition was performed on - (1) the normal heart region; (2) the region immediately surrounding the infarct; and (3) the infarcted region - one, two, three and four weeks into MI development. The spectral data were divided into six subgroups according to the histopathological features associated with various degrees / severities of myocardial tissue injury as well as various stages of myocardial tissue remodeling, post infarction. Various data processing and analysis techniques were employed to recognize the representative spectral features corresponding to various histopathological features associated with myocardial infarction. The identified spectral features were utilized in discriminant analysis to further evaluate their effectiveness in classifying tissue injuries induced by MI. In this study, it was observed that MI induced significant alterations (p < 0.05) in the diffuse reflectance spectra, especially between 450 nm and 600 nm, from myocardial tissue within the infarcted and surrounding regions. In addition, MI induced a significant elevation in fluorescence intensities at 400 and 460 nm from the myocardial tissue from the same regions. The extent of these spectral alterations was related to the duration of the infarction. Using the spectral features identified, an effective tissue injury classification algorithm was developed which produced a satisfactory overall classification result (87.8%). The findings of this research support the concept that optical spectroscopy represents a useful tool to non-invasively determine the in vivo pathophysiological features of a myocardial infarct and its surrounding tissue, thereby providing valuable real-time feedback to surgeons during various surgical interventions for MI.

Neodymium isotopic characterization of Ross Sea Bottom Water and its advection through the southern South Pacific, POLARSTERN cruise ANT-XXVI/2

Since the inception of the international GEOTRACES program, studies investigating the distribution of trace elements and their isotopes in the global ocean have significantly increased. In spite of this large-scale effort, the distribution of neodymium isotopes (143Nd/144Nd) and concentrations ([Nd]) in the high latitude south Pacific is still understudied. Here we report dissolved Nd isotopes and concentrations from 11 vertical water column profiles from the south Pacific between South America and New Zealand. Results suggest that Ross Sea Bottom Water (RSBW) is represented by an epsilon-Nd value of ~ -7, and is thus more radiogenic than Circumpolar Deep Water (epsilon-Nd ~ -8). RSBW and its characteristic epsilon-Nd signature can be traced far into the SE Pacific until progressive mixing with ambient Lower Circumpolar Deep water (LCDW) dilutes this signal north of the Antarctic Polar Front (APF). The SW-NE trending Pacific-Antarctic Ridge restricts the advection of RSBW into the SW Pacific, where bottom water density, salinity, and epsilon-Nd values of -9 indicate the presence of bottom waters of an origin different from the Ross Sea. Neodymium concentrations show low surface concentrations and a linear increase with depth north of the Polar Front. South of the APF, surface [Nd] is high and increases with depth but remains almost constant below ~1000 m. This vertical and spatial [Nd] pattern follows the southward shoaling density surfaces of the Southern Ocean frontal system and hence suggests supply of Nd to the upper ocean through upwelling of Nd-rich deep water. Low particle abundance dominated by reduced opal production and seasonal sea ice cover likely contributes to the maintenance of the high upper ocean [Nd] south of the APF. The reported data highlights the use of Nd isotopes as a water mass tracer in the Southern Ocean, with the potential for paleocenaographic reconstructions, and contributes to an improved understanding of Nd biogeochemistry.

Shorelines beneath the sea: Geomorphology and characterization of the postglacial sea-level lowstand, Cumberland Peninsula, Baffin Island, Nunavut

This thesis presents the discovery of eight submerged deltas (-19 to -45m), the first documented submerged boulder barricade, a submerged sill platform and spits off the coast of Cumberland Peninsula, eastern Baffin Island, NU. The geomorphic characteristics of these features in relation to contemporaneous sea-level are presented and compared with the modern shore-zone. The submerged boulder barricade at Qikiqtarjuaq in the west indicates a -16 m sea level that isolated Broughton Channel from Baffin Bay to the north, changing the coastal dynamics from those observed at present. A shoreline deeper than -50 m planed off the fiord-mouth sill in Akpait Fiord and formed spits at -50 m and -30 m present depth. These features define a submerged shoreline gradient of 0.35 m/km to the east across northeastern Cumberland Peninsula. The linear gradient sediment supply requirements for delta formation suggest a synchronous lowstand, bracketed by ice margins and sourced from glacial outwash between 11.8-8.5 ka. This confirms the submergence trend hypothesized for eastern Cumberland Peninsula (Dyke, 1979).

High-resolution spatial-response measurements of optical nano-antennas in the visible

A few years ago, some of the authors of the paper demonstrated the resonance of optical antennas in the visible frequencies. The results of that paper were obtained using experimental techniques that were primarily developed for the measurement of antenna-coupled detectors in the infrared. In the present paper, we show the results of spatial-response mapping obtained by using a dedicated measurement station for the characterization of optical antennas in the visible. At the same time, the bottleneck in the spatial responsivity calculation represented by the beam characterization has been approached from a different perspective. The proposed technique uses a collection of knife edge measurements in order to avoid the use of any model of the laser beam irradiance. By taking all this into account we present the spatial responsivity of optical antennas measured with high spatial resolution in the visible.

Absolute calibration and characterization of the multiband imaging photometer for Spitzer. I. The stellar calibrator sample and the 24 μm calibration

We present the stellar calibrator sample and the conversion from instrumental to physical units for the 24 μm channel of the Multiband Imaging Photometer for Spitzer (MIPS). The primary calibrators are A stars, and the calibration factor based on those stars is 4.54 × 10^-2 MJy sr^–1 (DN/s)^–1, with a nominal uncertainty of 2%. We discuss the data reduction procedures required to attain this accuracy; without these procedures, the calibration factor obtained using the automated pipeline at the Spitzer Science Center is 1.6% ± 0.6% lower. We extend this work to predict 24 μm flux densities for a sample of 238 stars that covers a larger range of flux densities and spectral types. We present a total of 348 measurements of 141 stars at 24 μm. This sample covers a factor of ~460 in 24 μm flux density, from 8.6 mJy up to 4.0 Jy. We show that the calibration is linear over that range with respect to target flux and background level. The calibration is based on observations made using 3 s exposures; a preliminary analysis shows that the calibration factor may be 1% and 2% lower for 10 and 30 s exposures, respectively. We also demonstrate that the calibration is very stable: over the course of the mission, repeated measurements of our routine calibrator, HD 159330, show a rms scatter of only 0.4%. Finally, we show that the point-spread function (PSF) is well measured and allows us to calibrate extended sources accurately; Infrared Astronomy Satellite (IRAS) and MIPS measurements of a sample of nearby galaxies are identical within the uncertainties.

On the group delay statistics of few-mode fibres with intermediate linear mode coupling

We report an investigation on the statistics of group delay for few-mode fibres operating in the weak and strong linear coupling regimes as well as in the intermediate coupling regime. A single expression linking the standard deviation of the group delay spread to the fibre linear mode coupling is validated for any coupling regime, considering up to six linearly polarized guided modes. Furthermore, the study of the probability density function of the group delays allowed deriving and validating an analytical estimation for the maximum group delay spread as a function of linear mode coupling.

Artificial neural network nonlinear equalizer for coherent optical OFDM

We propose a novel low-complexity artificial neural network (ANN)-based nonlinear equalizer (NLE) for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) and compare it with the recent inverse Volterra-series transfer function (IVSTF)-based NLE over up to 1000 km of uncompensated links. Demonstration of ANN-NLE at 80-Gb/s CO-OFDM using 16-quadrature amplitude modulation reveals a Q-factor improvement after 1000-km transmission of 3 and 1 dB with respect to the linear equalization and IVSTF-NLE, respectively.

Capacity estimates for optical transmission based on the nonlinear Fourier transform

What is the maximum rate at which information can be transmitted error-free in fibre-optic communication systems? For linear channels, this was established in classic works of Nyquist and Shannon. However, despite the immense practical importance of fibre-optic communications providing for >99% of global data traffic, the channel capacity of optical links remains unknown due to the complexity introduced by fibre nonlinearity. Recently, there has been a flurry of studies examining an expected cap that nonlinearity puts on the information-carrying capacity of fibre-optic systems. Mastering the nonlinear channels requires paradigm shift from current modulation, coding and transmission techniques originally developed for linear communication systems. Here we demonstrate that using the integrability of the master model and the nonlinear Fourier transform, the lower bound on the capacity per symbol can be estimated as 10.7 bits per symbol with 500 GHz bandwidth over 2,000 km.

Kerr-induced nonlinearity reduction in coherent optical OFDM by low complexity support vector machine regression-based equalization

We experimentally demonstrate 7-dB reduction of nonlinearity penalty in 40-Gb/s CO-OFDM at 2000-km using support vector machine regression-based equalization. Simulation in WDM-CO-OFDM shows up to 12-dB enhancement in Q-factor compared to linear equalization.

Anodic formation and characterization of nanoporous InP in aqueous KOH electrolytes

The anodic behavior of highly doped (> 1018 cm-3) n-InP in aqueous KOH was investigated. Electrodes anodized in the absence of light in 2- 5 mol dm-3 KOH at a constant potential of 0.5- 0.75 V (SCE), or subjected to linear potential sweeps to potentials in this range, were shown to exhibit the formation of a nanoporous subsurface region. Both linear sweep voltammograms and current-time curves at constant potential showed a characteristic anodic peak, corresponding to formation of the nanoporous region. No porous region was formed during anodization in 1 mol dm-3 KOH. The nanoporous region was examined using transmission electron microscopy and found to have a thickness of some 1- 3 μm depending on the anodization conditions and to be located beneath a thin (typically ∼40 nm), dense, near-surface layer. The pores varied in width from 25 to 75 nm and both the pore width and porous region thickness were found to decrease with increasing KOH concentration. The porosity was approximately 35%. The porous layer structure is shown to form by the localized penetration of surface pits into the InP, and the dense, near-surface layer is consistent with the effect of electron depletion at the surface of the semiconductor.